1. Field of the Invention
The invention relates to an ink composition, an ink for inkjet recording and an ink set using the same.
2. Description of the Related Art
Recently, materials for forming color images are specifically used as mainstream image recording materials. Specifically, inkjet type recording materials, thermosensitive transfer type image recording materials, electrophotographic recording materials, and the like are actively used. Inkjet recording methods have been rapidly coming into wide use and are further being developed since the costs for the materials are inexpensive, high-speed recording may be performed, there is little noise during recording, and color recording may be readily performed.
Aqueous ink compositions that are generally used in inkjet recording materials and the like have drawbacks in that the water resistance is deteriorated and bleeding tends to occur when printing is performed on plain paper, and in that when printing is performed on a non-water absorbing recording medium such as plastics, an image may not be formed due to poor adhesion of ink droplets, the recorded materials should be dried without being stacked immediately after printing since the solvent dries extremely slowly, and the images readily bleed.
In order to solve the problems concerning the drying property of ink, a method using a volatile organic solvent as a solvent for ink has been used. However, in order to dry quickly, it is necessary to use a solvent having a very high volatility such as methyl ethyl ketone or ethanol as a primary component.
As a method using an organic solvent, a method using a pigment as a colorant component is known (see Japanese Patent Application Laid-Open (JP-A) No. 5-214279). However, since the method uses a microparticle pigment in the form of a dispersion, aggregation of the pigment readily occurs, and inkjet nozzles are clogged, which makes stable ejection of the ink difficult. Furthermore, the method has a problem in that aggregation and the like of the ink are readily generated after long-term storage.
Moreover, the method also has a problem in that when a pigment is used as a colorant component, a desired color image quality is difficult to obtain due to insufficient color tone.
Furthermore, in order to obtain high image quality, high water resistance and high light fastness, an ink composition comprising an oil-soluble dye has been suggested (for example, see JP-A No. 2003-221530). However, the light fastness of the composition tends to be inferior to that of a pigment.
The invention aims to provide an ink composition that cures with a high sensitivity, has a high density, has an excellent light fastness and can form an image having a favorable color tone, and specifically, an ink useful for inkjet recording.
Furthermore, the invention aims to provide an ink set comprising the ink that cures at a high sensitivity, has a high density, has an excellent light fastness and can form an image having a favorable color tone.
The inventors have found that the above-mentioned problems can be solved by using an oil-soluble dye having a specific structure having an excellent light resistance as a coloring component in combination with a pigment. Since the invention has such a structure, a higher density than that of a conventional ink comprising only a pigment can be provided, the hue is easily adjusted, and the contrast can also be improved.
Namely, the means for solving the problems are as follows.